Alite

– Composition and Structure:
– Alite in Portland cement has a complex composition with CaO and SiO as major components.
– The formula of alite includes minor amounts of other oxides like MgO.
– Substitution of calcium ions or orthosilicate ions in alite must maintain electric charge balance.
– Limited substitution of orthosilicate ions with sulfate ions is possible in alite.
– Alite composition varies with the bulk composition of the clinker within certain limits.

– Polymorphs:
– Tricalcium silicate is unstable below 1250°C but can be preserved at room temperature by fast cooling.
– Slow cooling of tricalcium silicate leads to the formation of belite and CaO.
– Polymorphs of tricalcium silicate differ structurally due to minor deformations.

– Hydration Steps:
– Alite is crucial in Portland cement for setting and early strength development.
– Belite contributes to late strength due to lower reactivity.
– High alite reactivity is achieved by retaining high temperature polymorphs.
– Initial hydration of C involves partial dissolution of superficial oxide ions.
– Calcium silicate hydrate (C-S-H) phase provides strength to the hydrated cement system.

– Alite as Precursor of Silicate Phases in Medieval Lime Mortar:
– Alite rich in CaO and poor in SiO may form directly by pyrolizing siliceous limestone.
– Medieval lime mortars with unexpected hydraulic properties contain silicate phases formed by high-temperature reactions.
– Tournaisian limestones rich in amorphous silica were used for building lime mortar in the Tournai area.
– Presence of wollastonite and rankinite in medieval lime mortars indicates high-temperature reactions.
– Hydraulic properties of lime mortar in Tournai may have been developed unintentionally.

– Detection:
– Refer to the article on belite for more information.https://en.wikipedia.org/wiki/Alite